As a soldering metal for use in producing an optical device, such as a die bond for a Ga, As chip, there is an Au-20 wt % Sn soldering metal (referred to only as “An—Sn soldering metal” or only as “soldering metal” below) comprising 80% by weight of Au (gold) and 20% by weight of Sn (tin). The Au—Sn soldering metal is processed to a foil form, when using it for example for the above-described die bond for a Ga, As chip. Generally, the soldering is automatically performed with a soldering machine. A so-called ribbon-form Au—Sn soldering metal, which is a foil web or elongated foil form, is needed for the continuous soldering.
The ribbon-form Au—Sn soldering metal has conventionally been produced for example in a following manner. A metal ingot having 80% by weight of Au and 20% by weight of Sn is first cast through melt-casting, and the resultant ingot is rolled out. A foil-form soldering metal (a soldering metal having a thickness of for example 20 μm to 100 μm) obtained via the rolling is slit to a desired width to obtain a ribbon-form Au—Sn soldering metal.
However, the Au—Sn soldering metal as a workpiece, which is obtained through rolling an ingot, has properties of being brittle in room temperature and easily cracked. Therefore, if the slitting is applied to the soldering metal in room temperature, the soldering metal tends to be easily cracked at its edges during processing.
The crack occurs not only at the slitting but also at the rolling which is further performed when a thinner foil-form soldering metal is required, or at the blanking for producing a pattern-shape soldering metal for use, for example, in sealing the seal part of IC packages.
If the crack occurs, the ribbon-form soldering metal tends to be broken from the crack during or after processing. Therefore, it is difficult to work into a ribbon-form soldering metal or a foil-form soldering metal for sealing through the processing such as slitting, rolling or blanking in room temperature.
On the other hand, there is a processing method for hot working the foil-form soldering metal into a ribbon-form soldering metal or the like, and crack is relatively hard to occur according to this method. Slitting is described below as an example. For example, when the Au—Sn soldering metal as a workpiece obtained through rolling an ingot has a thickness of approximately 30 μm or more (generally 100 μm or less), a ribbon-form soldering metal can be produced through applying the slitting having a width of approximately 0.5 mm. However, for hot working such as hot slitting, a large scale apparatus is required, such that it is necessary to add facilities for heating an Au—Sn soldering metal and working tools such as a slitting blade, a reduction roll and a punch for blanking, or it is necessary to put working devices in an oil bath. Further, the processability for handling the soldering metal is very bad around the devices to which the heating facilities are added or which are in the oil bath. Therefore, the setting of the Au—Sn soldering metal as a workpiece to the device is difficult. In particular, when the thickness is approximately 20 μm or less, the setting of the soldering metal to the slitting device is difficult due to a low strength. Further, even if the setting is possible, the soldering metal tends to be cracked or broken during processing, so that it is hard to work it into a ribbon web or a pattern-shape soldering metal for sealing having a narrow part. In addition, there is a disadvantage that the processing operation becomes complicated such that regulation of the heating temperature is required for obtaining stable processing quality.
The present invention has been made in the above background, and it is an object of the present invention to provide a processing method capable of processing an Au—Sn soldering metal having a foil form in room temperature.